30 



SYSTEMATIC ZOOLOGY 



chitinous membrane or capsule pierced by holes. These two 

 parts of the protoplasm are therefore known as the intracap- 

 sular and the extracapsular respectively. Within the capsule 

 lies a large nucleus or several nuclei, together with oil globules, 

 granules, vacuoles, and sometimes minute crystals. The extra- 

 capsular protoplasm is generally filled with large, globular vacu- 

 oles, non-contractile, and beyond the free surface project the 



radiating pseudo- 

 podia (Fig. 10). 

 There is gener- 

 ally a siliceous 

 skeleton, though 

 not always, and 

 this varies greatly 

 from simple, 

 loosely arranged 

 spicules to very 

 elaborate, lattice- 

 work structures 

 (Fig. 1 1 ) resem- 

 bling helmets, 

 spheres, stars, and 

 in some cases 

 of 

 concentric 



3^>P* 





■-,■ ■ ■ \ 



■ ' > I . \ \ 



Fig. io. 



Thalassicola felagica, a Rudiolarian. 

 from Hatschek's Lehrbuch.) 



(After Haeckel, 



consisting 



three 



spheres pierced by numerous openings and radiating spicules 

 (Fig. 12). In many of the Radiolaria there occur yellowish 

 granules in the extracapsular protoplasm, which have long been 

 known as the "yellow cells." They are minute algae which live 

 with these Radiolaria in a state of symbiosis, a term applied to 

 the intimate association of two organisms to their mutual advan- 

 tage. Although, like most of the Rhizopoda, the members of this 

 order live as separate individuals, in a few cases colonies are 

 formed, and a number of individuals lie inclosed in a common 

 extracapsular mass (Fig. [3). These colonies are sometimes 

 macroscopic, being several centimeters in diameter. The re- 

 production of the Radiolaria, so far as it is known, differs from 

 that of the other Rhizopoda in the method of spore formation. 

 The spores are formed entirely in the intracapsular protoplasm ; 



